The written words in the Lotus Sutra are those words are in themselves the Buddha's mind

A person can know another's mind by listening to the voice. This is because the physical aspect reveals the spiritual aspect. The physical and spiritual, which are one in essence, manifest themselves as two distinct aspects; thus the Buddha's mind found expression as the written words of the Lotus Sutra. These written words are the Buddha's mind in a different form. Therefore, those who read the Lotus Sutra must not regard it as consisting of mere written words, for those words are in themselves the Buddha's mind. 5/6

The Writings of Nichiren Daishonin
Opening the Eyes of Wooden and Painted Images
Recipient unknown; written in 1264